While it is clear that more people now live longer than ever before in history, it is less obvious that this is a blessing. In Greek mythology, Tithonus was the mortal lover of Eos, goddess of the dawn. Eos asked Zeus to make Tithonus immortal but failed to mention “eternal youth,” dooming Tithonus to an eternity of physical and mental decay. The tithonean account of aging echoes loudly in the literature of the psychological and brain-sciences, which portrays adulthood as a protracted episode in mental decline, in which memories dim, thoughts slow, and problem-solving abilities diminish (Deary et al., 2009; Naveh-Benjamin & Old, 2008), and where researchers seem to compete to set the advent of cognitive decrepitude at an ever younger age (Salthouse, 2009; Singh-Manoux et al., 2012). Thus, although studies indicate that older adults are, on average, happier than younger adults (Charles & Carstensen, 2010), in the light of the foregoing, even this small crumb of comfort might be seen as further evidence of their declining mental prowess.

That's a quote from the start of a new paper by Michael Ramscar, Peter Hendrix, Cyrus Shaoul, Petar Milin, and Harald Baayen: "The Myth of Cognitive Decline: Non-Linear Dynamics of Lifelong Learning", Topics in Cognitive Science 2014. But as its title suggests, the paper argues that the conventional view is wrong, and the effects of aging on cognitive test results are mostly not the result of neural decay, but rather the consequence, put crudely, of knowing more stuff.

Their abstract:

As adults age, their performance on many psychometric tests changes systematically, a finding that is widely taken to reveal that cognitive information-processing capacities decline across adulthood. Contrary to this, we suggest that older adults’ changing performance reflects memory search demands, which escalate as experience grows. A series of simulations show how the performance patterns observed across adulthood emerge naturally in learning models as they acquire knowledge. The simulations correctly identify greater variation in the cognitive performance of older adults, and successfully predict that older adults will show greater sensitivity to fine-grained differences in the properties of test stimuli than younger adults. Our results indicate that older adults’ performance on cognitive tests reflects the predictable consequences of learning on information-processing, and not cognitive decline. We consider the implications of this for our scientific and cultural understanding of aging.

As I understand it, their model explains several otherwise-puzzling phenomena, including one that I discussed a few years ago in "Words and age", 12/23/2009. Roughly, if you probe word knowledge by asking people to go from words to meanings (as in typical vocabulary tests), average performance increases up to age 80, in the absence of dementia; but if you ask people to go from meanings to words (as in picture naming or category listing), average performance declines from the mid-30s on, with the decline accelerating through the 50s, 60s and 70s.

For those of us in increasing need of the Brain Alert Team, this a comforting theory. We're not getting slower and more forgetful, we're just getting more knowledgeable.

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"You see," he explained, "I consider that a man's brain originally is like a little empty attic, and you have to stock it with such furniture as you choose. A fool takes in all the lumber of every sort that he comes across, so that the knowledge which might be useful to him gets crowded out, or at best is jumbled up with a lot of other things so that he has a difficulty in laying his hands upon it. Now the skilful workman is very careful indeed as to what he takes into his brain-attic. He will have nothing but the tools which may help him in doing his work, but of these he has a large assortment, and all in the most perfect order. It is a mistake to think that that little room has elastic walls and can distend to any extent. Depend upon it there comes a time when for every addition of knowledge you forget something that you knew before. It is of the highest importance, therefore, not to have useless facts elbowing out the useful ones."
– A Study in Scarlet

Mark Meckes said,

@Ray: Although as I read the abstract, Holmes didn't have it quite right. The walls may well be elastic (though one assumes there must be a limit). The real issue seems to be that the fuller the attic, the more time it takes to sort through all the stuff for the item you need. The analogy resonates more for me personally if you replace "attic" with "garage", but it's certainly relatable.

Roy S said,

Those tip-of-the-tongue moments seem to be getting more frequent for me, too. That person whose name I'm sure I know, the snippet of melody I can almost place, the word perfectly describing the scene – the information is in there, it's just a matter of finding it. If we could defrag our brains like we can our hard drives, we might not need the pendant!

I've wondered if the brain could be a crowd of active agents working in parallel, with short term memory being a sort of pseudo-Cartesian theatre (with room for seven-plus-or-minus-two actors). So someone on the stage calls out for the name of something, and someone in the audience has that information and comes to the stage to provide it. Only as the audience grows, it takes longer for a spectator to make their way to the stage.

@Roy S: I figure much of the value of my brain, to the extent it has some, is in the unique organization of the stuff I've accumulated there over the decades. So I'd rather fumble for names than lose that uniqueness to defragging.

MattF said,

There's another, not unreasonable, theory about what happens when you age– which supplies the climax of the plot of Huxley's "After Many A Summer Dies The Swan." I won't spoil the ending, but you can look it up on Wikipedia.

@Ray Girvan: In later stories, Holmes gives more or less the opposite view, that it's worthwhile to know all sorts of seemingly useless information. He also shows knowledge in areas where he initially claimed to be completely ignorant. In particular, he knows a fair amount about astronomy, despite claiming (right around the quoted passage) not to have even known that the Earth goes around the Sun. If this is not to be seen as a straight-out retcon, the only logical conclusion is that in A Study in Scarlett, Holmes is simply messing with Watson, who he has only just met.

Mark F. said,

It would be interesting to see whether, for people at the same age, words-to-meanings performance anticorrelates with meanings-to-words performance. I've done well at the former but poorly at the latter since well before my mid-thirties.

Steve said,

This reminds me of a good line from a short lived sci-fi TV show from the 1990s (IIRC), which, like a current show, involved a human cop who is partnered with an android. The human cop, who has been repeatedly shown up by the smarty-pants android, stumps "her" on a (IIRC) question of sports trivia. He smugly says something like, "Oh, I guess you don't know everything!" Genuinely baffled, she replies, "It would be impractical to know everything: the access time would be horrendous."

Chris C. said,

@Brett — It may also be that Holmes' view on the subject evolved as he grew older and more experienced as a consulting detective. Holmes was a relatively young and unknown when Watson met him: In "His Last Bow", set in 1914, Holmes is said to be 60 years old, and "A Study in Scarlet" has Holmes meeting Watson in 1881, making him 27 at the time.

Or Doyle just forgot later on. Either way.

I'm reminded a little more strongly of Robert Heinlein's millennia-old Lazarus Long, who in Time Enough for Love complains of having too many memories to easily retrieve despite having his memory re-catalogued with machine assistance. That's more about past events than language, though, and in extremis Lazarus is depicted as reverting to his native early 20th century Missouri dialect.

Mar Rojo said,

And what about memories of things that you thought were your own but were not, so to speak?

Oliver Sacks experienced this phenomenon:

One night, a thousand-pound bomb fell into the garden next to ours, but fortunately it failed to explode. All of us, the entire street, it seemed, crept away that night (my family to a cousin’s flat)—many of us in our pajamas—walking as softly as we could (might vibration set the thing off?). The streets were pitch dark, for the blackout was in force, and we all carried electric torches dimmed with red crêpe paper. We had no idea if our houses would still be standing in the morning.

On another occasion, an incendiary bomb, a thermite bomb, fell behind our house and burned with a terrible, white-hot heat. My father had a stirrup pump, and my brothers carried pails of water to him, but water seemed useless against this infernal fire—indeed, made it burn even more furiously. There was a vicious hissing and sputtering when the water hit the white-hot metal, and meanwhile the bomb was melting its own casing and throwing blobs and jets of molten metal in all directions.

A few months after the book was published, I spoke of these bombing incidents to my brother Michael. Michael is five years my senior, and had been with me at Braefield, the boarding school to which we had been evacuated at the beginning of the war (and in which I was to spend four miserable years, beset by bullying schoolmates and a sadistic headmaster). My brother immediately confirmed the first bombing incident, saying, “I remember it exactly as you described it.” But regarding the second bombing, he said, “You never saw it. You weren’t there.”

I was staggered by Michael’s words. How could he dispute a memory I would not hesitate to swear on in a court of law, and had never doubted as real? “What do you mean?” I objected. “I can see the bomb in my mind’s eye now, Pa with his pump, and Marcus and David with their buckets of water. How could I see it so clearly if I wasn’t there?”

Mar Rojo said,

And lastly: "We, as human beings, are landed with memory systems that have fallibilities, frailties, and imperfections—but also great flexibility and creativity. Confusion over sources or indifference to them can be a paradoxical strength: if we could tag the sources of all our knowledge, we would be overwhelmed with often irrelevant information."

– Sacks

exackerly said,

The one that bothers me is making homophone mistakes while typing. I never did that until a couple of years ago, and I don't make any other kind of spelling errors. There's at least one study that identifies this as a marker for early onset Alzheimer's.

Terry Hunt said,

At the risk of deviating from the main trajectory of Mark Liberman's Original Post, "In later stories, Holmes gives more or less the opposite view . . . In particular, he knows a fair amount about astronomy . . ." could simply reflect that since his earlier statement Holmes has found reason to study the subject.

This might be expected, since his arch-antagonist, the mathematician Professor Moriarty, turns out to have published a monograph entitled (from memory) On the Dynamics of an Asteroid.

Whether, as has been conjectured, Moriarty planned to destroy the Earth by deflecting an asteroid into a collision, or more plausibly blackmail governments with that threat, is unconfirmed in the available papers of The Biographer (ACD), but the point remains that Holmes' acquiring new knowledge as necessary over the course of his career is entirely consistent with his original assertion.
That said, I still like to think that during their early relationship, Holmes was messing with Watson's head.

Chris C. said,

@Mar — I think that's an entirely different phenomenon. I have at least one false memory myself, but rather than being a problem of retrieving a datum from an increasingly large welter of information, I think they're from vivid misimpressions or imagined incidents from early in life which are soon after misapprehended as genuine memories.

The false memory I mentioned above had to have been formed when I was about 3 years old, and I recognized it as false by my early teens when confronted with the concrete reality of what I was remembering, so it's not a function of advancing age.

P said,

I like the basic idea of the paper because the actual age-related decline in intelligence seems to be less than what some psychometric tests indicate. However, the level of confidence they have in their findings is not consummate with the evidence they have. They use simulations rather than actual data and consider only a very limited set of tests.

In particular, they don't really address the main facts discovered in psychometric aging research, namely that "crystallized" intelligence measures show little age-related decline, while "fluid" measures do show such decline. In particular, performance on tests with minimal verbal demands (say, Raven's, block design, mental rotation, reaction time) clearly declines with age, and this study says nothing about it. Some of their claims, such as that one's knowledge of one rare word is not predictive of their knowledge of other rare words, are almost certainly false.

The Sherlock Holmes quote is good and seems to describe something that I experience as I get older, except that the brain's refusal to store any old rubbish is not really under my control, it is an acquired instinct. If I want to persuade my brain to store irrelevant facts I have to constuct contexts for them.

I think of it as like a compiler, a young brain has a powerful compiler but a poor or non-existent optimiser so it soaks up any information it can get, but an older brain maybe isn't so speedy on the front end but it has a very efficient optimiser and knows how to make best use of resources. So if you put older people in a class with younger people they may appear to learn more slowly if the teaching methods are designed for younger people. But with the right study methods they can learn as fast or faster. I started learning Mandarin at the age of 50 so I had to work this stuff out for myself!